The present invention relates to a golf ball material which has good flow properties and moldability, and can be used to obtain high-performance golf balls endowed with excellent properties such as rebound resilience, durability, flexibility and scuff resistance. The invention also relates to a method of preparing such a golf ball material.
In recent years, ionomeric resins have been widely used in golf ball materials. Ionomeric resins are ionic copolymers of an olefin such as ethylene with an unsaturated carboxylic acid such as acrylic acid, methacrylic acid or maleic acid, in which some of the acidic groups are neutralized with metal ions such as sodium, lithium, zinc or magnesium. These resins have excellent characteristics in terms of the durability, rebound resilience and scuff resistance of the ball.
At present, the base resins used in golf ball cover materials are generally ionomeric resins, but various modifications are being made to address the constant desire by players for golf balls having a high rebound and an excellent flight performance. Recently, a number of approaches are being carried out to achieve a higher ball rebound in particular: blending together different ionomers, blending an ionomer with another thermoset resin and additives, and increasing the degree of neutralization of the ionomer itself.
One example of an improved ionomeric resin composition is the ionomeric resin composition disclosed in U.S. Pat. No. 5,312,857 which is obtained by blending from 25 to 75 parts by weight of a stearic acid metal salt with 100 parts by weight of ionomer.
In addition, JP-A 2000-93557 discloses art that increases ball rebound through the use of a material obtained by mixing a stearic acid metal salt with an ionomer that is a metal salt of a terpolymer.
However, in the foregoing ionomeric resin compositions, the ionomer serving as the base resin has a poor compatibility with various additives such as the stearic acid metal salt and the degree of increase in ionomer neutralization is excessive, resulting in a ball durability that is less than adequate.